1. Field of the Invention
The present invention relates to an imaging device having a live view display function, and to a control method for the imaging device, and in detail relates to an imaging device, having a so-called live view display function (also called an electronic viewfinder function) for displaying an image acquired by an image sensor on a display unit, capable of focusing a photographing lens using an image signal during this live view display, and to a control method for an imaging device.
2. Description of the Related Art
In a conventional digital camera, observation of a subject image is performed using an optical viewfinder. Recently however, digital camera are available on the market that do not have an optical viewfinder, or as well as the optical viewfinder have a live view display function for displaying an image that has been acquired by an image sensor using a display device such as a liquid crystal monitor for subject observation.
A digital camera having this type of live view display function is useful in making subject observation easy because a subject image acquired by the image sensor is displayed directly. However, in a digital single lens reflex camera, in order to carry out live view display a movable mirror that is arranged in the imaging optical path is temporarily retracted, which means that during live view it is no longer possible to use an AF (Auto Focus) mechanism that employs a conventional phase difference method where an amount of defocus of the photographing lens is detected using subject light flux that has been reflected by a sub-mirror attached to the moveable mirror.
For example, a digital single lens reflex camera that uses both contrast AF for performing AF by detecting contrast information based on an image signal from an image sensor, and the phase difference method AF, is disclosed in Japanese unexamined patent application No. 2006-163094 (laid-open Jun. 22, 2006). With this digital single lens reflex camera, focusing of the photographing lens is carried out using contrast AF once at the time of performing live view display, in response to an operation of pressing the release button down half way.